1. Field of the Invention
The present invention pertains to the preparation of rigid cellular foams. More particularly, the present invention relates to the preparation of rigid cellular foams characterized by carbodiimide linkages. Even more particularly, the present invention relates to the preparation of rigid cellular foams characterized by carbodiimide linkages from catalyst-reactant systems.
2. Prior Art
There has been disclosed heretofore the preparation of rigid cellular foams characterized by carbodiimide linkages. See, inter alia, U.S. Pat. Nos. 3,645,923; 3,717,596; 3,772,217; 3,723,366, etc. Generally, these compositions are prepared by the catalytic condensation of an organic polyisocyanate in the presence of a carbodiimide catalyst, such as a 2,4,6-tris(dialkanolamino)-s-triazine.
To promote the incorporation of isocyanurate groups into the resulting foams, the prior art, as exemplified above, has taught the use of co-catalyst systems comprising a carbodiimide catalyst and an isocyanate trimerization catalyst. The use of trimerization catalysts, while enhancing the flame retardancy of the foams, provides highly crosslinked polymers. As a result thereof, the foams produced from such co-catalyst systems tend to be characterized by high friability. This, in turn, necessitates the use of friability decreasing additives and the like, thereby increasing the cost of such foams.
Recognizing the fact that carbodiimide catalysts do, in and of themselves, cause trimerization of isocyanates, it would be most beneficial to employ such catalysts in combination with other catalysts or reactants which would negate the problems of friability while not diminishing the inherent qualities of the foams under consideration herein. It is to this end to which the present invention is directed.